Anti-aircraft sighting device



Feb. 28, 1967 K. G. F. LIND I AIRCRAFT SIGHTING DEVICE ANTI 2Sheets-Sheet 1 Filed May 26, 1965 j, Y i r EVVENTOR KARL G/AN FOL/ 5L/ND BY f A T Tak/vs Y:

Feb. 28, 1967 K. G. F. UND 3,307,180

ANTI'AIRCRAFT SIGHTING DEVICEV Filed May 26, 1965 2 Sheets-Sheet 2F/2c05 V H J/ mvm'mn KAR/ GRAN Fo/.KE wp y Y EL i A -r Tak/VE ns UnitedStates Patent Ofice 3,307,180 ANTI-AIRCRAFT SIGHTING DEVICE Karl GoranFolke Lind, Karlskoga, Sweden, assignor to Aktiebolaget Bofors, Bofors,Sweden, a company of Sweden Filed May 26, 1965, Ser. No. 458,922 Claimspriority, application Sweden, June 3, 1964, 6,767/ 64 7 Claims. (Cl.343-14) The present invention is related to an anti-aircraft sightingdevice, in particular a radar sighting device, of the type provided withan equipment for automatic target tracking, which comprises inconventional manner servomotors for laying the sight proper, that is theradar antenna in a radar sighting device, in azimuth and elevationrespectively and for setting a range measuring unit, which servomotorsare supplied with control signals from the sighting device representingthe azimuth angular deviation and the elevation angular deviationrespectively between the actual direction of the sight and the truedirection to the target and the difference between the range presentlyset in the range measuring unit and the true range to the target, sothat the servomotors will endeavor continuously when the target ismoving to keep the sight directed upon the target and the rangemeasuring unit set upon the true range to the target. For the largevelocities of modern air targets a very large ampliiication and a fastresponse should be required in the abovementioned servocircuits in orderto obtain a sufficiently accurate target tracking. The control signalssupplied from the sighting device to the servomotors, which arerepresenting the errors in the direction of the sight and in the settingof the range measuring unit, comprise, however, and this is inparticular true for radar sighting devices such disturbances that theservo-circuits, in which these control signals are used, cannot be givena large amplication and a rapid response. In order to solve thisproblem, at least partially, the sighting device can be provided with aspecial computer arranged to compute on the basis of the target datadetermined by the sighting device and a certain assumption regarding themovement of the target some suitable regenerative control signal for theservo-motors so that these will automatically, without any assistance ofthe error signals from the sighting device, keep the sight directed uponthe target and the range measuring unit set upon the range to thetarget, so long as the target is moving in the manner assumed. Then theerror signals from the sight have only to provide a correction of thedirection of the sight and the setting of the range measuring unit, ifthe target is deviating from the assumed manner of movement, whereforethe servo-circuits for these error signals do not have to be providedwith a large amplification factor and a rapid response. Hitherto one hasgenerally arranged the computer to calculate the azimuth angularvelocity and the elevation angular velocity of the target about theazimuth axis and the elevation `axis of the sight as regenerativecontrol signals for the assumption that the target is moving in astraight course with a constant velocity, and these regenerative controlsignals have been supplied to the servomotors laying the sight inazimuth and in elevation respectively. With the Very large velocities ofmodern air targets, however, the targets display considerable azimuthangular accelerations and elevation angular accelerations and alsosignificant radial accelerations relative to the sighting device, inparticular when the targets are passing close to the sighting device. Ifthe regenerative control signals are representing the calculated valuesfor the azimuth angular velocity and the elevation angular velocity ofthe target, no consideration will be paid to the abovementionedaccelerations of the target. Further- 3,307,180 Patented Feb. 28, 1967more, the assumption that the target is moving in a straight course witha constant velocity is not realistic under all circumstances as modernair-targets have in many cases, for instance during dive attacks, aconsiderable acceleration in the direction of the course liight. It has,therefore, turned out to be impossible to achieve a suiciently accuratetarget tracking in direction and in range by the aid of regenerativecontrol signals representing the elevation angular velocity and theazimuth angular Velocity of the target and calculated with theassumption that the target is moving in a straight course with aconstant velocity.

The object of the present invention is therefore to provide ananti-aircraft sighting device of the type mentioned in the introductionand in particular a radar sighting device of this type, vwhich providesan improved automatic target tracking, particularly for targets passingclose to the sighting device and having an accelerated motion.Characteristic for the sighting device according to the invention isthat it comprises an electric computer, preferably an analogue computer,which is supplied with data determined by the sight regarding theazimuth angle, the elevation angle and the range to the target and alsothe azimuth angular velocity, the elevation angular velocity and theradial or range velocity of the target with respect to the site of thesighting device and which is arranged to compute on the basis of saiddata and the assumption that the targe is moving in a straight coursewith a variable velocity the azimuth angular acceleration of the targetabout the azimuth axis of the sight and the elevation angularacceleration of the target about the elevation axis of the sight and toproduce signals proportional to the calculated azimuth angularacceleration and the calculated elevation angular accelerationrespectively, which signals are applied as regenerative control signalsto the servomotor laying the sight in azimuth and to the servomotorlaying the sight in elevation respectively.

When considered necessary, the computer can be arranged to compute onthe basis of the above mentioned assumption regarding the movement ofthe target also the radial or range acceleration of the target withrespect to the site of the sighting device and to produce a signalproportional to said calculated range acceleration, to be lapplied as aregenerative control signal to the servomotor setting the rangemeasuring unit. Under most circumstances, however, the rangeacceleration of the target is considerably smaller than the elevationangular acceleration and the azimuth angular acceleration of the targetand a certain error in the target tracking in range is also generallyless serious than an error inthe target tracking in azimuth and inelevation, wherefore in many cases it can be suilicient to calculate theazimuth angular acceleration and the elevation angular acceleration ofthe target and to produce signals proportional thereto to be used asregenerative control signals -for the servomotors laying the sight inazimuth and elevation.

The invention gives an accurate target tracking without any assistancefrom the error signals from the sighting device, even if the targetdisplays very large -azimuth angular acceleration, elevation angularacceleration and range acceleration with respect to the sight and has anaccelerated movement, provided that it is 4moving in a straight courseand consequently its acceleration is in the direction of Hight. Theassumption that the aircraft is moving in a straight course and that itsacceleration vector is lying in the `direction of this course iscertainly not correct under all circumstances, but will in the practicenot cause -any serious errors, as one is interested in an accuratetarget tracking above all immediately before and during the ring at thetarget and the target is in most 3 cases ired at, at least when it comesto light anti-aircraft artillery, when the target itself is attackingand consequently generally ilying in a 4straight course.

It turns out that the expressions for the azimuth angular acceleration,the elevation angular acceleration and the range acceleration of thetarget with respect to the sight are comparatively simple also with theassumption that the target is moving with a variable velocity in astraight course, Wherefore the sighting devicewaccording to theinvention becomes comparatively simple, -compact and cheap. According tothe invention the computer is consequently arranged to calculate thevalue of the expression as a measure for the azimuth Iangularacceleration of the target about the azimuth axis of the sight, tocalculate the value of the expression 1?"Z F l as a measure for theelevation angular acceleration of the target about the elevation axis ofthe sight and possibly also to calculate the value of the expressionl/iz-tazmv COS www] as a measure for the range acceleration of thetarget with respect to the site of the sight. In these expressions Fl isthe total velocity of the target or the component of its velocity in apredetermined direction, Fl the total acceleration of the target r thecomponent of its acceleration in said predetermined direction, Al therange from the sight to the target as determined by the sight, the rangeor radial velocity of the target as determined by the sight, zv theelevation angle to the target as determined by the sight with respect tothe plane in which the sight is ylaid in azimuth, liv the elevationangular velocity of the target as determined by the sight about theelevation axis of the sight and sv the azimuth angular velocity of thetarget as determined by the sight about the azimuth axis of the sight.

For the quantity Fl/Fl the computer is preferably arranged to determinethe ratio between the acceleration component of the target which isparallel with the azimuth laying plane of the sight and the velocitycomponent of the target in the same direction.

In order to obtain .an accurate control of the servomotors by theregenerative control signals representing the calculated accelerationsof the target in the different coordinate directions, the servomotorsmust be provided with feedback. Preferably each regenerative controlsignal is supplied to the associated servomotor through an integratorand a signal generator is coupled to the servomotor for producing asignal proportional to the speed of the servomotor and this signal isfed back negatively or in opposition to the servomotor. As analternative the regenerative control signal can be applied directly tothe associated servomotor, in which case a signal generator is coupledto the servomotor for producing a signal proportional to theacceleration of the servomotor and this acceleration signal is fed backnegatively to the servomotor.

In the following the invention will be yfurther described with referenceto the enclosed drawing, in which FIG. 1 shows `schematically by way ofexample an anti-aircraft radar sighting device according to theinvention;

FIG. 2 is a projection of the movement of the target and therelationship between the target and the sight in the plane, in which thesight is laid in azimuth, that is in a plane perpendicular to theazimuth axis of the sight. In the following it will be assumed for thesake of simplicity that the azimuth axis of the sight is vertical andthat consequently the sight is laid in azimuth in the horizontal plane;

FIG. 3 is a corresponding projection of the movement of the target andthe relationship between the target and the sight in a plane containingthe direction from the sight to the target and the azimuth axis of thesight; that is a vertical plane containing the direction to the sight,if the azimuth axis of the sight is vertical as assumed above;

FIG. 4 shows in perspective the relationship between the sight and thetarget and the directions of the different coordinate velocities of thetar-get, and

FIG. 5 shows more in detail t-he electric analogue computer in thesighting device shown in FIG. 1.

The anti-aircraft sighting device shown in FIG. l Cornprises inconventional manner ya radar antenna A, which is pivoted in a stand 2 ona platform 1, as schematically shown in the drawing. The platform 1 isjournalled in a support structure 3 so that it can be rotated togetherwith the antenna. For the sake of simplicity it is assumed that theplatform 1 can be rotated about a vertical axis. The -antenna A ismounted in the stand 2 so that it can be pivoted about an axisperpendicular to the axis of rotation of the platform ll, that is abouta horizontal axis in the assumed case. The antenna A can consequently belayed in azimuth as well as in elevation in a conventional manner. Theantenna is laid in elevation by means of a servomotor SH and in azimuthby means of a servomotor SS rotating the platform i1. The antenna A isin a conventional manner connected to a transmitterreceiver equipment Rfor radar signals. The transmitterreceiver equipment R comprises aran-ge measuring unit, which can be operated or set by means of aservomotor SA. The radar sight is in any conventional manner designedfor automatic target tracking, that is the transmitter-receiverequipment R comprises means for producing a first error signal esrepresenting the azimuth angular deviation between the actual directionof the antenna A and the true direction to the target M, a second errorsignal eh representing in the same way the elevation angular deviationbetween the actual direction of the antenna and the true direction tothe target and a third error signal ea representing the differencebetween the range set in the range measuring unit and the true range tothe target. The error signal es is connected through an adder circuit 4to the servomotor SS as a control signal therefor and the servomotor SSwill consequently endeavor to rotate the platform 1 and thereby lay theantenna A in azimuth so that the error signal es is maintained zero,that is so that the vantenna is kept directed upon the target M inazimuth. In a corresponding way the erro-r signal eh is connectedthrough an adder circuit S to the servomotor SH laying the antenna A inelevation so that this servomotor will endeavor to keep the antennadirected upon the target in elevation. The error signal ea -is connectedthrough a corresponding adder circuit 6 as a control signal to theservomotor SA, which will consequently endeavor to keep the rangemeasuring unit set on the true `range to the target. Tachogenerators T1,T2 and T3 are coupled to the servomotors SS, SH and SA and Igenerateconsequently signals representing the rates of rotation of theservomotors, that is the elevation angular velocity and the azimuthangular velocity of the antenna and the rate of change of the setting ofthe range measuring unit respectively. These signals are connectedthrough the adder circuits 4, 5, 6 to the associated servomotors SS, SHand SA as negative feedback. signals. As previously mentioned, ltheerror signals 68 eh and 6 contain such disturbances that theservo-circuits,` in which these control signals are used, cannot begiven a sucient amplification and a suticiently rapid response so thatthe antenna and the range measuring unit under the inuence of thesecontrol signals are brought toI track a target accurately, which ispassing close to the sight with large velocity.

In order to remedy this disadvantage, the sighting device according tothe invention is provided with -a computer K, preferably an electricanalog computer, which is supplied from the sight with the target datadetermined by the sight, viz. the azimuth angle sv, the elevation an-glehv and the range Al to the targe and the azimuth angular velocity s`v,the elevation yangular velocity liv and the range velocity I :of thetarget. As the computer K is an electromechanical analog computer, theValues for the azimuth angle sv, the elevation angle hv and the range Alrespectively, are conveyed from t-he sight to the computer by means ofmechanical connections from t-he shafts of the servomotors SS, SH and SAto those electromechanical computer elements in the computer, as forAinstance potentio'meters and resolvers, which are to be adjusted inrelation to these values. In FIG. 1 these mechanical connections areindicated by dash-and-dot lines. Electrical signals representing theazimuth angular velocity s'v, the elevational angular velocity liv andthe range velocity l of the target are derived from the servo-circuitsfor the servomotors SS, SH and SA in a manner to be described in detailin the following and are in the computer K connected as control signalsto servomotors, which operate those electromechanical computercornponents, potentiometers -and similar, in the computer, which are tobe set in agreement with the azimuth angular velocity, the elevationangular velocity and the range velocity respectively. v

According to the invention the computer is arranged to calculate on thebasis of the target dat-a supplied from the sight the azimuth angularacceleration s'v of the target about the azimuth axis of the sight, theelevation angular acceleration of the target -about the elevation axisof the sight and the range acceleration Al of the target with respect tothe site of the sight for the assumption that the target is moving in astraight course with variable velocity, and to produce signalsproportion-al to said quantities. These signals :are used asregenerative control signals for the servomotors SS, SH and SA and areconnected to the associated servomotor through an integrator Il, I2 andI3 respectively and the corresponding adder circuit 4, 5 and 6respectively. Each integrator is additionally supplied with thecorresponding error signal es, eh and sa respectively from the targettracking equipment of the radar station R. Assuming that the errorsignals es, eh and ea respectively from the target tracking equipment inunit R are zero, that is that the antenna is directed accurately towardsthe target and the range measuring unit is set accurately on the rangeto the target, the integral from anyone of the integrators I1, I2, I3 ofthe corresponding regenerative control signal-s proportional to thecalculated acceleration of the target in the corresponding coordinatedirection will obviously control the 'associated servomotor SS, SH andSA respectively together with the feed back signal from thecorresponding tachogenerator T1, T2 and T3 respectively, and theservomotors will consequently keep the antenna directed towards thetarget and the range measuring unit set on the range to the target withlarge accuracy, so long as the target is moving in the manner assumed,that is in a straight course. The error signals es, eh and sa from thetarget tracking equipment of the radar station need consequently to beused only for the correction of errors in the regenerative control ofthe servomotors, which -arise when the target is not moving in theassumed manner or are caused by inaccuracies in the regenerative controlof the servomotors, which arise when the target is not moving in theassumed manner or are caused by inaccuracies in the regenerativecontrol. It can be shown that the output signals from the integratorsI1, I2 and I3 are with good accuracy representing the azimuth angularvelocity and the elevation angular velocity of the antenna and the rateof change of the setting of the range measuring unit respectively, thatis these signals represent the azimuth angular velocity, the elevationangular velocity and the range velocity respectively 4of the target,wherefore these signals are supplied to the computer K as measures forthese target data. The shown design of the servo-circuits gives also agood filtering of the radar noise, which should in other cases appear inthese signals supplied to the computer K.

In the embodiment of the invention shown in FIG. 1 the azimuth angularvelocity and the elevation angular velocity of the antenna A and thus ofthe target are determined by means of direct voltage tachogenerators T1yand T2 coupled to the servomotors SS and SH. This is advantageous, asdirect voltage tachogenerators can be given a high accuracy. ,Theservo-circuits in FIG. l are consequently direct voltage servo-circuits.It is understood, however, that the feedback signals produced by thetachogenerators T1 and T2 should also be achieved by means of angularvelocity sensitive gyros mounted on the platform 1 and the elevatingmass of the antenna A respectively. Furthermore it is obvious that eachfeedback signal can be composed of several signals derived fromdifferent signal generators, which signals together represent theazimuth angular -velocity or the elevation angular velocity respectivelyof the antenna with respect to the ground, if the antenna platform 1 ismounted on a movable support. It is also obvious that the regenerativecontrol signals can be connected directly to the associated servomotors,if these are provided with signal generators producing signalsproportional to t-he -azimuth angular acceleration and the elevationangular acceleration respectively of the antenna. It is, however,dilicult to obtain accelerometers with the same high accuracy Iastachogenerators.

As already mentioned is it not always necessary that the servomotor SAfor the range measuring unit is supplied with a regenerative controlsignal from the cornputer K, as in most cases the range acceleration ofthe target is considerably smaller than its azimuth angular accelerationand elevation angular acceleration and las the demand for -accuracy isnormally less in the target tracking in range than in the targettracking in direction.

The expression to be computed by the computer K for the azimuth angularacceleration of the target about the azimuth axis of the sight can bededuced from FIG. 2, which is a projection in the horizontal plane,assumed to be perpendicular to the azimuth axis of the sight, of themovement of the target and the relationship between the target and thesite of the sight. In FIG. 2, S designates the site of the sight`and Mthe target. The azimuth Vangle in the horizontal plane between thedirection to the target and a fixed reference direction O is designatedwith sv. The horizontal range between the sight and the target isdesignated with Ah and the horizontal velocity component of the targetwith Fh.

FIG. 2 gives directly where Fh and Ah are functions of the time.Derivation of the expression (2) gives and if this relation is insertedin the expression (3) one obtains Fh sin gh Fh sin c Q.

Fh Ah Ah Ah Aha (5) If the relations (1) and (2) are inserted in theabove expressions (5), one obtains h 215th 81)- S1) (6) Furthermore onehas that Ah=Al cos hv (7) -hv tan hv Fh l sv 2E+hv tan hv sv (lo) whichis consequently the expression to be calculated by the computer K forthe azimuth angular acceleration Irv of the target about the azimuthaxis of the sight.

The expression to be `calculated by the computer K for the elevationangular acceleration of the target about the elevation axis of the sightcan be deduced from FIG. 3, which shows the projection of the movementof the target and the relation between the site of the sight and thetarget in a vertical plane containing the direction to the target. Samereference characters are used in FIG. 3 as in FIG. 2 and furthermore Hdesignates the horizontal plane, hv the elevation angle for thedirection to the target relative to the horizontal plane, Al theslanting range from the site of the sight to the target, and Fv thevertical velocity component of the target.

FIG. 3 gives directly Fh cos o sin hv Al (11) where Fh, FV, qu, hv andAl are functions of the time.

FIG. 3 also gives l=Fh cos q cos hv-i-Fv sin hv Derivation of theexpresion (11) gives Fv eos hv (13) As it is assumed that the target ismoving in a straight course, the total velocity and the totalacceleration of the target has the same direction and the followingrelation is consequently true.

n hj Fv-Fh F (14) where F is the total velocity of the target and F thetotal acceleration of the target. It is also obvious that the same ratiois achieved between any acceleration component of the target and thevelocity component of the target in the same direction as theacceleration component. Insertion of the relation (14) in the expression(13) gives By using the realtions (l), (2), (7), (ll) and (12) in thisexpression, one obtains ab an Fh Al (16) which is consequently theexpression to be calculated by the computer K for the elevation angularacceleration hv of the target about the elevation axis of the sight.

The expression possibly to be calculated by the computer K for the rangeacceleration of the target with respect to the site of the sight can beobtained by derivation of the expression (12), which gives hv: )hv-(sv)2 sin hv cos hv Anl=lih cos p cos hv-l-Fv sin hv-i-Fh ip sin p coshv-l-Fh hv cos e sin hv-i-Fv hv cos hv (17) By inserting the relations(l), (2), (7), (l1), (l2) and (14) in this expression, one obtains whichis consequently the expression for the range acceleration Al of thetarget, which is to be calculated by the computer K, if a regenerativecontrol signal is required also for the servomotor operating the rangemeasuring unit.

As understood from the above relation (14) and what has been said inconnection with this relation, the quantity Ih/Fh in the aboveexpression (l0), (16) and (18) for the azimuth angular acceleration, theelevation angular acceleration and the range acceleration respectivelyof the target can in principle be replaced by the ratio liv/ F v betweenthe vertical acceleration of the target and the vertical velocity of thetarget `or by the ratio lil/F, between the total acceleration of thetarget and the total velocity of the target or by the ratio between anyother acceleration component of the target and the velocity component inthe same direction as the acceleration component. It is, however,important that the acceleration component and the velocity component arechosen in such a direction that the ratio between them does not becomeindefinite for a certain type of movement of the target. For this reasonthe ratio v/Fv is inexpedient, as this ratio will obviously becomeindeiinite, as soon as the target course is horizontal. From this pointof view it should be most advantageous to use the ratio I"/F between thetotal acceleration of the target and the total velocity of the target,as this ratio is never indeiinite. To evaluate the total velocity of thetarget requires however more extensive arithmetic operations than toevaluate its horizontal velocity, wherefore it is preferable to use theratio F11/Fh between the horizontal acceleration and the horizontalvelocity of the target. This is possible, as this ratio will be indeniteonly if the target has a vertical or substantially vertical course,which is a very unlikely type of movement for the target.

Regarding the various quantities contained in the above deducedexpressions (l0), (16) and (18) for the azimuth angular accelerations'v', the elevation angular acceleration hv and the range accelerationof the target following quantities are directly determined by the sightand supplied to the computer K, viz. the range Al to the target, therange velocity l` of the target, the elevation angle hv to the target,the elevation angular velocity liv of the target and the azimuth angularvelocity s'v of the target. Regarding the value for the horizontalvelocity Fh of the target this must however be calculated by thecomputer. The expression for the horizontal velocity Fh ofthe target canbe deduced from FIG. 4, which shows in perspective the relationshipbetween the target M and the site S of the sight and the differentcoordinate velocities of the target determined by the sight, viz. theazimuth angular velocity v, the elevation angular velocity hv and therange of velocity l.

9 From FIG. 4 it can be seen that the target has a horizontal Velocitycomponent in the direction perpendicular to the projection Ah of thedirection to the target and that this velocity component has the valueAh s'v=Al sv cos hv (19) In addition thereto the target has a horizontalvelocity component, which is parallel to the horizontal projection ofthe direction to the target and has the value Al cos hv+Az iw sin 1w 20)Vectorial addition of these two mutually perpendicular velocitycomponents will give the total horizontal velocity Fh of the target,having consequently the expression mtg/(Azev @s hv 2+ (All @0S liv-All@sin m02 It requires consequently only one vector addition forcalculating the horizontal velocity of the target. In order to calculatethe total velocity of the target, however, it should be necessary tomake two vector additions, wherefore this is a more complicatedarithmetic operatlon.

FIG. shows a block diagram of the computer K for calculating the abovededuced expressions for the azimuth angular acceleration, the elevationangular acceleration and the range acceleration of the target and forproducing signal voltages proportional to said expressions to be appliedto the servomotors SS, SH and SA as regenerative control signals. Thecomputer is an electric analogue computer comprising as computercomponents essentially potentiometers, which are so designed and sooperated in dependence of the input data supplied to the computer thatthey have voltage divisions proportional to the quantities indicatedwithin each potentiometer symbol in FIG. 5. As already mentioned, thosepotentiometers which are to be set in dependence of the azimuth anglesv, the elevation angle hv and the range Al to the target aremechanically coupled to the servomotors SS, SH and SA respectively,whereas those potentiometers which are to be set in dependence of theazimuth angular velocity v, the elevation angular velocity liv and therange velocity Al of the target as determined by the sight are coupledto servomotors within the computer but not shown in the drawing, whichare controlled by the signals supplied to the computer from the sightand are representing the azimuth angular velocity, the elevation angularvelocity and the range velocity of the target respectively.

At terminal 7 the computer is supplied with a reference alternatingvoltage assumed for the sake of simplicity to have the amplitudevalue 1. This reference voltage is connected to a rst potentiometer P1having a voltage division proportional to the range AZ to the target.The voltage from the potentiometer P1 is connected to twoseries-connected potentiometers P2 and P3 having a voltage divisionproportional to the azimuth angular velocity s-v and to cos hvrespectively. The voltage from the potentiometer P3 is consequentlyproportional to Al sv cos hv. The voltage from the potentiometer P1 isalso connected to a potentiometer P4 having a voltage divisionproportional to the elevation angular velocity hv. The voltage from thepotentiometer P4 is consequently proportional to Al hv. The referencevoltage on terminal 7 is also applied to a potentiometer P5 having avoltage division proportional to the range velocity Al. The voltagesfrom the potentiometers P4 and P5 are connected to each one of the inputwindings of an electric resolver R1, the rotor of which is rotatedrelative to the stator of the resolver in agreement with the elevationangle hv to the target. The output voltage from the one output windingof the resolver R1 is consequently proportional to l cos hv-Al hv sinhv. This voltage and the voltage 10 from the potentiometer P3 areconnected to each one of the input terminals of a unit 8 of the typeproducing an output signal proportional to the square root of the sum ofthe squares of the two input quantities. The unit 8 can for instance beof the type described in any of the U.S. patent specications 2,600,264,2,781,169 and 2,997,- 236, but can of course also consist of some otherconventional device giving an output signal proportional to the squareroot of the sum of the squares of two input signals. The output voltagefrom unit 8 is consequently, according to the expression (21) above,proportional to the horizontal velocity Fh of the target. This outputvoltage is a direct voltage and is connected through an adder circuit 9as a control voltage to a servomotor SF. A potentiometer P6 suppliedfrom the terminal 10 with a reference direct voltage of the magnitude 1is coupled to the shaft of the servomotor SF. The voltage from thepotentiometer P6 is consequently proportional to the horizontal velocityFh of the target and this voltage is fed back in opposition to theservomotor SF through the adder circuit 9 and is also connected to adiiferentiating circuit 11 producing consequently an output voltageproportional to the horizontal acceleration component Fh of the target.This voltage is also fed back in opposition to the servomotor SF throughthe adder circuit 9, whereby an accurate speed control of the servomotoris achieved. The voltage from the differentiating circuit 11, obviouslybeing a direct voltage, is connected to a modulator M1, the outputalternating voltage of which is connected to a potentiometer P7, whichis coupled to the shaft of the servomotor SF and has a voltage divisionproportional to 1/Fh. The alternating voltage from the potentiometer P7is consequently proportional to h/Fh.

For the calculation of the azimuth angular acceleration sv of the targetthe computer comprises a potentiometer P8 having the voltage division1/Al and being supplied with the voltage proportional to l from thepotentiometer P5. The voltage from the potentiometer P8 is con- 12. Thevoltage proportional to Fh/Fh from the potentiometer P7 is alsoconnected to this adder circuit. The adder circuit 12 is designed to addthe supplied input voltages with the mutual proportions and polaritiesindicated at the input terminals of the adder circuit. The outputvoltage from the adder circuit 12 is connected to a potentiometer P12having the voltage division v. The alternating voltage fromthepotentiometer P12 is consequently, according to the above expression(10), proportional to the calculated azimuth angular acceleration sv ofthe target. As the voltage from the potentiometer P12 is an alternatingvoltage, whereas the regenerative control signal for the azimuth layingservo of the antenna must -be a direct voltage signal, the voltage fromthe potentiometer P12 is connected to a demodulator D1, which givesconsequently a direct voltage proportional to the computed azimuthangular acceleration sv of the target.

For the calculation of the elevation angular acceleration liv of thetarget the computer comprises a potentiometer P13 having the voltagedivision (v)2, which is supplied from the reference alternating voltageon terminal 7. The output voltage of this potentiometer is applied to apotentiometer P14 having the voltage division cos hv. The voltage fromthe potentiometer P14 is connected to an additional potentiometer P15having the voltage division sin hv. The output Voltage from thispotentiometer is consequently proportional to (av)2 sin hv cos hv.Furthermore, the computer comprises an adder circuit 13 having as inputvoltages the voltage proportional to Al/Al from the potentiometer P8 andthe voltage proportional to Fh/Fh from the potentiometer P7. The addercircuit 13 is designed to add the two input voltages with the mutualproportions and polarities, indicated at the input terminals of theadder circuit, wherefore the output voltage from the adder circuit 13 isproportional to F/t/Fh-ZAl/Al. This voltage is connected to apotentiometer P16 having the voltage division liv. The output voltage ofthis potentiometer is connected to an additional adder circuit 14together with the voltage from the potentiometer P15. The adder circuit14 is designed to add the two input voltages with the mutual proportionsand polarities indicated at the input terminals of the adder circuit,wherefore the output voltage from the adder circuit 14 will, accordingto the above expression (16), be proportional to the calculatedelevation angular acceleration lv of the tar-get. The output alternatingvoltage from the adder circuit 14 is connected'to a demodulator D2,which gives consequently an output direct voltage proportional to thecomputed elevational angular acceleration llv of the target. c

For the calculation of the range acceleration Al of the target withrespect to the site of the sight the computer comprises a potentiometerP17 having the voltage division Al and being fed with the voltageproportional to Fh/Fh from the potentiometer P7. The output voltage fromthis potentiometer is consequently proportional to l Fit/F11.Furthermore, the computer comprises a potentiometer P18 having thevol-tage division liv and being fed with the voltage proportional to hvfrom the potentiometer P9. The voltage from the potentiometer P18 isconsequently proportional to (7Lv)2. An additional potentiometer P19having the voltage division cos zv is fed with the voltage from thepotentiometer P14, wherefore the output voltage from the potentiometerP19 is proportional to (sv cos hv)2. This voltage is together with thevoltage from the potentiometer P18 connected to an adder circuit 15,which is adding the two voltages with the mutual proportions andpolarities indicated at the input terminals of the adder circuit. Theoutput voltage from the adder circuit is connected to a potentiometerP20 with the voltage division Al. The output voltage from thepotentiometer P20 is consequently proportional to Al[(sv cos hv)2+hv2].This voltage is together with the Voltage from the potentiometer P17connected to an adder circuit 16, which is adding the two voltages withthe mutual proportions and polarities indicated at the input terminalsof the adder circuit, wherefore the output voltage from the addercircuit 16 will, according to the above expression (18), be proportionalto the computed range acceleration Al of the target. The alternatingvoltage from the adder circuit 1'6 is connected to a demodulator D3,which produces consequently an output direct voltage proportional to thecomputed range accele-ration Al, which direct voltage can be connectedas regenerative control signal to the servomotor SA.

lIt should be noticed that the electric analog computer for thecalculation of the azimuth angular acceleration, the elevation angularacceleration and the range acceleration of the target, which isschematically shown in FIG. 5 and described above, is only an example ofa computer suitable for this purpose. The same arithmetic operations canof course be made also by a computer of a different type or design.

I claim:

1. An anti-aircraft sighting device comprising, in cornbination: a sightlayable in azimuth and elevation for determining the direction to atarget, an automatic target tracking equipment for measuring the rangeto the target and for generating error signals representing the azimuthangular deviation and the elevation angular deviation between thedirection of the sight and the direction of the target and the deviationbetween the range presently Set in said tracking equipment and the rangeto the target, servomotors controlled by said error signals for layingsaid sight in azimuth and elevation and for setting the range in saidtracking equipment, means associated with the sight and the trackingequipment for producing target data signals representing the azimuthangle, the elevation angle, and the range to the target and the azimuthangular velocity, the elevation angular velocity and the range velocityof the target in relation to the site of the sight, an electric computersupplied with said target data and arranged to compute on the basis ofsaid data and the assumption that the target is moving in a straightcourse with a variable velocity, the azimuth angular acceleration andthe elevation angular acceleration of said target and to produce signalsproportional to said computed azimuth angular acceleration and saidcomputed elevation angular acceleration respectively, said signals beingconnected to the servomotor laying said sight in azimuth and theservomotor laying said sight in elevation respectively as regenerativecontrol signals for said servomotors.

2. An anti-aircraft sighting device as `claimed in claim 1, wherein said`computer is arranged to compute on the basis of said target data and ofan assumption that the target is moving in a straight course withvariable velocity, also the range acceleration of said ltarget and toproduce a signal proportional to said computed range acceleration, saidsignal being applied as a regenerative con trol signal to the servomotorfor setting said range rneasuring unit.

3. An anti-aircraft sighting device as claimed in claim 1, andcomprising an integrator, each one of said regenerative control signalscomputed and produced by said computer -being connected to theassociated servomotor through said integrator, and wherein means areprovided for generating signals proportional to the rate of change inthe azimuth angle and the elevation angle respectively of said sighteffected by the operation of said servomotors, said signals being fedback to the corresponding servomotors in opposition.

4. An anti-aircraft sighting device as claimed in claim 1, wherein saidcomputer is arranged to calculate a iirst expression l il -QE-l-Ww tanhv sv and a second expression at n ITL 2A-Z)hv (sv) sin 1w cos lwwherein Fl is the acceleration of the target in a predetermineddirection, Fl is the velocity of the target in said predetermineddirection, Al is the range to the target as determined by said sight, lis the range velocity as determined by the sight, hv is the elevationangle to the target as determined 'by the sight with respect to theplane in which the sight is laid in azimuth, liv is the elevationangular velocity of the target as determined by said sight about theelevation axis of the sight and v is the azimuth angular velocity of thetarget as determined 'by said sight about the azimuth axis of the sight,and wherein a computer is arranged to produce first and second signalsproportional to said rst and second expression respectively, said firstsignal being applied as a regenerative control signal to the servomotorlaying said sight in azimuth and said second signal being applied as aregenerative control signal to the servomotor laying said sight inelevation.

and to produce a third signal proportional to said third expression,said .third signal being applied as a regenerative control signal to theserVomot-or operating said range measuring unit.

46. An anti-aircraft sighting device as claimed in claim 4, wherein saidcomputer is arranged to calculate the quantity Fh/Fh, Where Fh is thevelocity component of the target parallel to the azimuth plane of saidsight and Fh' is the acceleration component of the target in the samedirection as said velocity component, and to use said quantity as thequantity F l/F l when calculating said first and second expressions.

14 7. An anti-aircraft sighting device as claimed in claim 6, whereinsaid computer is arranged to calculate the expression computer as ameasure for the quantity Flr/Fh.

No references cited.

CHESTER L. IUSTUS. Primary Examiner. T. H. TUBBESING, AssistantExaminer.

1. AN ANTI-AIRCRAFT SIGHTING DEVICE COMPRISING, IN COMBINATION: A SIGHTLAYABLE IN AZIMUTH AND ELEVATION FOR DETERMINING THE DIRECTION TO ATARGET, AN AUTOMATIC TARGET TRACKING EQUIPMENT FOR MEASURING THE RANGETO THE TARGET AND FOR GENERATING ERROR SIGNALS REPRESENTING THE AZIMUTHANGULAR DEVIATION AND THE ELEVATION ANGULAR DEVIATION BETWEEN THEDIRECTION OF THE SIGHT AND THE DIRECTION OF THE TARGET AND THE DEVIATIONBETWEEN THE RANGE PRESENTLY SET IN SAID TRACKING EQUIPMENT AND THE RANGETO THE TARGET, SERVOMOTORS CONTROLLED BY SAID ERROR SIGNALS FOR LAYINGSAID SIGHT IN AZIMUTH AND ELEVATION AND FOR SETTING THE RANGE IN SAIDTRACKING EQUIPMENT, MEANS ASSOCIATED WITH THE SIGHT AND THE TRACKINGEQUIPMENT FOR PRODUCING TARGET DATA SIGNALS REPRESENTING THE AZIMUTHANGLE, THE ELEVATION ANGLE, AND THE RANGE TO THE TARGET AND THE AZIMUTHANGULAR VELOCITY, THE ELEVATION ANGULAR VELOCITY AND THE RANGE VELOCITYOF THE TARGET IN RELATION TO THE SITE OF THE SIGHT, AN ELECTRIC COMPUTERSUPPLIED WITH SAID TARGET DATA AND ARRANGED TO COMPUTE ON THE BASIS OFSAID DATA AND THE ASSUMPTION THAT THE TARGET IS MOVING IN A STRAIGHTCOURSE WITH A VARIABLE VELOCITY, THE AZIMUTH ANGULAR ACCELERATION ANDTHE ELEVATION ANGULAR ACCELERATION OF SAID TARGET AND TO PRODUCE SIGNALSPROPORTIONAL TO SAID COMPUTED AZIMUTH ANGULAR ACCELERATION AND SAIDCOMPUTED ELEVATION ANGULAR ACCELERATION RESPECTIVELY, SAID SIGNALS BEINGCONNECTED TO THE SERVOMOTOR LAYING SAID SIGHT IN AZIMUTH AND THESERVOMOTOR LAYING SAID SIGHT IN ELEVATION RESPECTIVELY AS REGENERATIVECONTROL SIGNALS FOR SAID SERVOMOTORS.